Police are hoping that a baseball cap found inside a US zoo will help them track down the suspects in the beating death of a monkey.
A break-in at the zoo in Boise, Idaho left a Patas monkey dead from blunt force trauma to the head and neck.
Police are analysing blood found at the scene to determine if it came from the monkey or one of two human intruders.
Police said two males wearing dark clothing were spotted by a security guard outside the fence near the primate exhibit.
Both fled and police have been unable to find them.
But they said that a grey baseball cap with a skull design was probably left behind by one of them.